DE102008061743B4 - Process for the preparation of a hydraulically acting product - Google Patents

Abstract

Process for the preparation of a hydraulically acting product, in which a. a base component in the form of a carbonaceous compound having a carbon content of more than 10% by weight with b. at least one additional material selected from clay, oil shale burn, limestone, gypsum and combustion residues from coal power plants having a carbon content of less than 10 wt .-% is mixed, and then the mixture in a fluidized bed at a temperature of 600 to 900 ° C. is fired to the hydraulically acting product, wherein the at least one additional material is used in a wet state with a water content of up to 25 wt .-%, to lower the furnace temperature below 900 ° C.

Description

The present invention describes a process for the production of hydraulically acting products, such as cement or cement substitutes, based on carbonaceous compounds having a carbon content of more than 10 wt .-%, wherein the carbonaceous compounds in an oven at a temperature of 750 to 900 ° C to be burned.

For the production of cement or cement substitutes carbonaceous compounds are used. As such raw material oil shale is often used, which refers to those clayey rocks containing bitumen or heavy oils as a collective term. The proportion of organic material, the so-called kerogen, depending on the occurrence between 10 and 30 wt .-%.

Like in the DE 385 624 A is described in the production of cement from oil shale, the oil is first driven out of the oil shale by smoldering. Subsequently, the coal left behind in the oil shale is burned and a carbon-free cement mass is formed, which is converted into ready-to-use cement by grinding.

From the GB 951 211 A It is also known to mix mineral oil substances such as lime or clay before the carbonization of the oil shale and to pellet the mixture and then to calcine it at a temperature of 400 ° C. in order to remove the organic constituents.

In connection with the increasing scarcity of fossil raw materials, the generation of energy by burning the oil shale is becoming increasingly important. The combustion takes place, for example, as in the DE 38 22 999 C1 describe, via a fluidized bed combustion. This allows a very good heat exchange and thus a very homogeneous temperature profile over the entire fluidized bed.

The burning of the oil shale in the furnace results in a product containing clinker phases. These consist in particular of dicalcium silicate and Monocalciumaluminat, but it is found in addition to free calcium oxide and calcium sulfate, a larger proportion of pozzolanic reactive oxides such as silica. The resulting product therefore reacts with water and lime to a water-insoluble compound, which opens up applications as a cement or cement substitute.

However, when burnt oil shale for producing cement or cement substitutes, the high energy input of the oil shale into the furnace poses problems, since temperatures below 900 ° C are needed to achieve a high quality product, the pozzolanic and hydraulic properties for later use in concrete production sure.

It has therefore been tried in various ways to lower the temperature in the oven. Frequently, the temperature control is carried out by discharging energy from the furnace by means of membrane walls or Tauchheizflächen, as shown in the DE 34 47 186 A1 are described. The Tauchheizflächen are immersed in the fluidized bed of the furnace or a separate fluidized bed cooler and withdraw this by evaporation of a condensate energy. The generated steam can be used elsewhere for energy production. In addition to the disadvantage of increased investment costs due to an increased number of components, however, especially the contact of these heat-dissipating components with the hot solid is problematic, which leads to rapid wear of the cooling elements. Furthermore, the fluidized bed is cooled locally, which can lead to a more inhomogeneous product.

A similar problem of inhomogeneous temperature control is also found in the cooling with quench water, which also requires additional devices for venting the water vapor produced in large quantities.

A lowering of the furnace temperature can also be achieved by increasing the amount of combustion air and thus a reduced local density of the fluidized bed or by flue gas recirculation. However, the disadvantage here is the lower space-time yield and the significantly increased dimensioning of the system.

To further improve the material properties, it is about from the EP 0 727 398 B2 known to introduce additives in the product obtained by burning. As such additives, especially calicum sulfate or calcium sulfoaluminate are suitable, but also alumina, phosphonic acid derivatives and a number of polymers can be used. An end product produced in this way often shows attractive chemical properties in terms of construction chemistry, in particular in its capacity as composite cement with low setting times.

The DE 12 51 688 B describes the production of cement clinker in a vortex furnace. The use of this type of furnace means that even materials with comparatively low calorific value, in particular clay and limestone, can be burned. There is no indication of the use of moist educts. On the contrary, attention is drawn to the necessary upstream expulsion of chemically bound condensed water.

Also the DE 24 20 121 A1 deals with the use of feedstocks with low calorific value. These materials should already be introduced into the leading from the rotary kiln to the lowest stage of preheating gas line and burned there, so as to produce without additional combustion chamber, hot gas for the operation of the furnace. The introduction of materials with a residual water content is not mentioned.

From the DE 603 02 138 T2 The use of fly ash and cement floor dust in the production of clinker materials is known, but also here all materials are introduced dry. Attention is drawn to the problem of introducing moisture into the process.

The DE 198 33 447 C2 addresses the use of soot and other waste materials in a cement production process. Again, the material can not be introduced moist into the process, but the interposition of a predrying is provided with appropriate water content.

From the DE 196 22 591 A1 there is known a process for the production of Portland cement clinker which utilizes wastes from the paper industry. This can be a both material and thermal recovery of these substances used, although these waste materials still have a water content of 35-65%. The material is fed directly into the primary or secondary waste heat system of the rotary kiln used, resulting in an explosive evaporation of the water contained, which distributes the solid in fine particles throughout the kiln system and thus completely burns it.

The object of the present invention is therefore to allow a uniform reduction of the furnace temperature without additional equipment in the production of hydraulically acting products from raw materials with a high calorific value.

This object is achieved with the invention essentially by the features of claim 1.

All additional materials are materially inert, or low in calorific value, thereby lowering the temperature created by the combustion of the high-carbon raw materials in the furnace by dilution of the solid phase. Although this reduces the space-time yield in terms of energy yield, the pure energy yield relative to the starting material is kept constant. The addition of additional materials increases the product output relative to the amount of carbon-rich raw material used. In addition, material properties of the resulting product can be specifically varied.

Additives may already have cement properties before or after a thermal treatment. Under cement properties is understood here that it is a hydraulically acting binder, in particular for mortar and concrete, which hardens by addition of water by hydration water and preferably also resistant to space.

The carbonaceous material is in a particularly preferred embodiment of the invention oil shale, which has a high calorific value. But it is also possible to use from combustion residues such as ashes or soot, in particular combustion residues from coal power plants, with a comparatively high carbon content. The carbon content is more than 10 wt .-%, preferably more than 15 wt .-% and particularly preferably more than 20 wt .-%.

Lignite as a low-grade coal with a high moisture content of mostly more than 50 wt .-% is also suitable for use according to the invention as a burning material.

In order to simplify the handling and the apparatus design, the additional material is mixed with the material to be burned before it is introduced into the oven with this. As a result, a homogeneous mixture is introduced into the furnace, which also leads to a homogeneous temperature profile in the furnace.

In a further embodiment of the invention, the oven temperature can be additionally influenced by a connected circuit cooling. The prevailing temperatures of the solid streams correspond approximately to those of the desired furnace temperature. The additionally introduced into the process inert or Heizärwertarme material can be introduced in a development of the invention at a point of this cooling circuit before, in or after the cooler in the solids flow

In one embodiment of the invention clay is added which is used in cement production as a naturally occurring raw material and has pozzolanic properties.

A further embodiment of the invention provides for the addition of oil shale burn-up, which is particularly preferably produced as a residue of dust firing and generally has a residual carbon content of 2 to 5 wt .-% or more. In addition to hydraulic properties as aluminate, silicate and iron oxide supports the Admixture of oil shale waste the disposal (recycling) of a waste product and therefore offers a particular economic advantage.

A further embodiment of the invention relates to the addition of low-carbon combustion residues from coal power plants, in particular the so-called. Bottom-Ash, which have a similar composition as the oil shale burn and also hydraulic properties. Even more so than in the use of oil shale burnout here is the disposal of a problem waste material to emphasize, since such incineration residues are currently disposed of in landfills. The carbon content of these compounds is according to the invention below 10 wt .-%, preferably below 5 wt .-% and particularly preferably below 2.5 wt .-%.

Another embodiment of the invention involves the addition of limestone, which both reduces the sulfur content by deacidifying the limestone and then reacting the resulting calcium oxide with sulfur oxides, as well as increasing the bonding ability of the product.

Another embodiment of the invention describes the addition of gypsum, which acts as a binding retardant in the resulting end product.

It is within the scope of the invention that the above-described variants of the additional materials can be added to the oil shale in any combination with each other.

The invention provides for the addition of at least one of the admixed materials in the wet state. The water content of this material is up to 25 wt .-%, preferably up to 15 wt .-% and leads by calcination and / or evaporation to an additional energy discharge from the oven, whereby at the same time the proportion of the admixed material can be lowered ,

In a preferred embodiment of the invention, it is additionally provided that the solids stream consisting of the oil shale and the admixed additional material is heated before it enters the kiln. In this context, other pretreatments such as preheating of individual components are conceivable.

Show it:

1 schematically a plant for carrying out the method according to the invention and

2 the energy to be dissipated depending on the amount of inert material used (clay, moisture 20 wt .-%).

In 1 schematically a plant for carrying out the method according to the invention is shown.

In a mixing container 1 oil shale and clay are mixed and then via a supply line 2 a fluidized bed furnace 3 fed, in which the mixture is fired at a temperature of, for example, 800 ° C. The mixture can also be done by co-grinding or another type of pre-preparation.

The clay is dried and calcined at the temperature generated in the furnace by the combustion of the organic components of the oil shale. The quantities of oil shale and clay put into the kiln are determined by the amount of energy required for combustion, drying and calcining.

After combustion and calcination, the solids are removed via a discharge line 4 from the oven 3 deducted and, if necessary, after further treatment steps, such as grinding and mixing with cement clinker used as cement and, for example, used in concrete production.

The solids may be added before or after mixing in the mixing vessel 3 for example in a venturi preheater 5 to be preheated.

Instead of the illustrated stationary fluidized bed in the oven 3 Of course, a circulating fluidized bed or an annular fluidized bed can also be used for the combustion of the material.

Instead of clay and limestone, gypsum, oil shale burn and / or combustion residues from power plants can be added.

example

For the production of 12 t / h of fired oil shale, 16 t / h of oil shale with a moisture content of 7% by weight and an inlet temperature of 25 ° C. are introduced into an oven, for example a fluidized-bed furnace. Assuming a calorific value of 3400 kJ / kg, a drain of 4.3 MW is required to keep the furnace temperature below the product-damaging temperature of 900 ° C.

According to the method of the invention, the oil shale clay is added with a moisture content of 20 wt .-%. With the available amount of energy of 4.3 MW, approximately 3200 kg / h of the clay can be dried and calcined in the kiln.

2 shows in this connection the decrease of the energy to be dissipated in the oven as a function of the amount of wet clay used for the assumed moisture content of 20% by weight.

The use of the product mixture as a cement substitute is possible. The achieved product quantity can thus be increased by the invention with the same oil slate entry to 15.2 t / h. If, on the other hand, the total product volume of 12 t / h is kept constant, only about 9.475 t / h of oil shale and 2.525 t / h of clay have to be used.

LIST OF REFERENCE NUMBERS

1

mixing tank

2

supply line

3

oven

4

withdrawal line

5

preheater

Claims (6)

Process for the preparation of a hydraulically acting product, in which a. a base component in the form of a carbonaceous compound having a carbon content of more than 10 wt .-% with b. at least one additional material selected from clay, oil shale burn, limestone, gypsum and combustion residues from coal power plants having a carbon content of less than 10% by weight, is then mixed and the mixture is then fired in a fluidized bed furnace at a temperature of 600 to 900 ° C to the hydraulically acting product, wherein the at least one additional material is used in a wet state with a water content of up to 25 wt .-% to lower the oven temperature to below 900 ° C. A method according to claim 1, characterized in that oil shale is used as the carbonaceous compound. A method according to claim 1, characterized in that as a carbonaceous compound ashes with a carbon content of more than 10 wt .-% are used. A method according to claim 1, characterized in that are used as the carbonaceous compound carbon blacks having a carbon content of more than 10 wt .-%. A method according to claim 1, characterized in that are used as the carbonaceous compound combustion residues from coal power plants with a carbon content of more than 10 wt .-%. A method according to claim 1, characterized in that lignite is used as the carbonaceous compound.

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